Symmetry in Mesoscale Circulations Explains Weak Impact of Trade Cumulus Self‐Organization on the Radiation Budget in Large‐Eddy Simulations

Abstract We investigate if mesoscale self‐organisation of trade cumuli in 150 km‐domain large‐eddy simulations modifies the top‐of‐atmosphere radiation budget relative to 10 km‐domain simulations, across 77 characteristic, idealized environments. In large domains, self‐generated mesoscale circulations produce fewer, larger and deeper clouds, raising the cloud albedo. Yet they also precipitate more than small‐domain cumuli, drying and warming the cloud layer, and reducing cloud cover. Consequently, large domains cool slightly less through the shortwave cloud‐radiative effect, and slightly more through clear‐sky outgoing longwave radiation, for a net cooling (−0.5 W ). This cooling is generally smaller than the large‐domain radiation's sensitivity to large‐scale meteorological variability, which is similar in small‐domain simulations and observations. Hence, mesoscale self‐organisation would not alter weak trade‐cumulus feedback estimates previously derived from small‐domain simulations. We explain this with a symmetry hypothesis: ascending and descending branches of mesoscale circulations symmetrically increase and reduce cloudiness, weakly modifying the mean radiation budget.